At least some links within communication systems of a mobile platform, such as an aircraft, bus, ship or train, transmit signals at very high frequencies, e.g. greater than 1 GHz. Signals at such high frequencies can not be digitally sampled and therefore must be transmitted as an analog signal. Additionally, these high frequency signals often require a very high degree of transmission accuracy between various points of the mobile platform. For example, electronic warfare systems of an aircraft require a high degree of transmission accuracy. Currently, coaxial cable is typically used to provide such communication links. However, coaxial cable is costly and very heavy and thus adds production costs and weight to the mobile platform. To reduce this cost and weight, attempts have been made to incorporate fiber optic links in some known mobile platform communications systems. To date, implementation of fiber optics has been impeded by the inability to maintain linearity, i.e. transmission accuracy, between the high frequency electrical signal input to the communication system and the optical signal output from the communication system. That is, fiber optic communication systems within the mobile platform are generally not capable of converting such high frequency electrical signals to optical signals without degradation of the signal.
More specifically, in order to modulate a laser source at high frequencies, an external modulator is generally employed, for example a Mach-Zehnder interferometer. When using a modulation device, such as a Mach-Zehnder interferometer, the optical signal is modulated across one arm of the interferometer, thereby delaying the phase of the optical signal through that arm with respect to the other arm of the interferometer. As a result of the constructive or destructive interference, the optical signal output from the interferometer is amplitude modulated. However, the modulation of optical signals at high frequencies within a broad range of amplitudes is generally non-linear, i.e. the optical signals are generally distorted with respect to the electrical signal used to modulate the optical signal.
Therefore, it would be desirable to employ a fiber optic communication system within a mobile platform, wherein optical signals can be modulated within a wide range of frequencies and amplitudes without distortion. Thus, there would be very little degradation or distortion of the optical signals with respect to the electrical signal use to modulate the optical signal. Employing such fiber optics in certain mobile platform communication systems would save costs and considerably reduce the payload of the mobile platform.